How many common precision casting processes are there?

The shell making processes widely used in the production of precision castings in China are as follows: A. water glass shell; B. Composite shell; C. Silica sol shell (low-temperature wax); D. Silicone sol shell (medium temperature wax). The first three options all use low-temperature wax (molds).

1. The water glass shell process has a production history of nearly 50 years in China, and its factories still account for over 75% of investment casting manufacturers in China. After half a century of unremitting efforts from colleagues in the precision casting industry, the application research of water glass shell technology has reached a high level. Over the years, due to the improvement of refractory materials for the back shell and the promotion and application of new hardening agents, the strength of water glass shells has been doubled. The surface quality, dimensional accuracy, and yield of castings have greatly improved, still occupying a large market share, and replacing foreign sand casting exports in bulk. Low cost, short production cycle, excellent shelling performance, and high breathability are still advantages that no other shelling process can achieve so far. However, the quality of castings, including surface roughness, number of defects, dimensional accuracy, yield, and repair rate, is inferior to the other three processes.

2. In order to overcome the shortcomings of water glass shells mentioned above, many factories currently Both the layer and the second layer use zircon and mullite silica sol shells. The back layer still adopts the original water glass shell process. It is an improvement plan that combines the excellent surface quality of the silicone shell with the advantages of low cost and short cycle of water glass. Compared with the water glass shell, the surface quality of castings has been greatly improved, with reduced surface roughness, reduced surface defects, and reduced repair rates. It can be applied to high alloy steel such as stainless steel and heat-resistant steel. The production cycle is much shorter than that of low-temperature wax sol molds, similar to water glass molds.

3. The shell process of silica sol (low-temperature wax) is in line with national conditions. When casting medium and large castings weighing over 1kg, especially 5kg, it has greater adaptability and superiority (compared to medium temperature wax). Generally speaking, the quality requirements for medium to large castings, especially for surface roughness, dimensional accuracy, and geometric tolerances, are not too high, so it is not necessary to use high melting point medium temperature wax. Medium temperature wax requires high pressure (greater than 6-7MPa) or liquid wax injection into the wax mold, resulting in high equipment investment. Medium temperature wax thick and large wax molds are prone to shrinkage, sagging, deformation, and high cost. Low temperature wax is easy to form, with simple equipment, and the surface roughness of the wax mold does not differ significantly. This process is more stable in quality than composite molds, especially with high dimensional accuracy of castings, as it does not have water glass and the mold has good high-temperature performance. It can be used for thin-walled parts and small and medium-sized parts with complex structures, and can produce 50-100kg ultra large parts, such as water pumps, impellers, guide sleeves, pump bodies, ball valve bodies, and valves. For thin-walled, small, medium, and large parts, fork shells or lifting shells can be directly cast in front of the furnace to achieve high yield.

4. Silicone sol (medium temperature wax) mold shell is a universal precision casting production process. Having The casting quality and The repair rate is particularly suitable for small and medium-sized parts with high surface roughness requirements (Ra0.8-3.2) and high dimensional accuracy (CT3-CT5), as well as very small parts (2-1000g grade). However, due to equipment and cost limitations, medium to large items (5-100kg) are less commonly used.